Print shops or companies that operate internal publication operations look for ways to reduce expenses associated with the reproduction of documents for the company or customers. One area that impacts expenses is the ability to be able to print both grayscale and color documents. Grayscale documents are typically printed by printing pixels of different densities of black ink on white paper. The density of the ink or toner for a pixel is defined by a binary value for the pixel. Color documents may be generated by printing pixels of different densities of at least two colors of ink or toner. When the pixels are formed from black ink and another color of ink, the color documents are typically called duotone or highlight documents. Sometimes duotone documents also refer to documents having pixels comprised of two colored inks and a black ink. Full color documents are comprised of pixels having four different colored inks. Typically, these four inks are cyan, magenta, yellow, and black and the printers used to produce full color documents are known as CMYK or four color printers.
Colored documents are more expensive to generate than grayscale documents because more than one colorant is required and the size of each color component in pixel must be determined and generated during the printing process. Control of the printer to apply the inks in these measured amounts to achieve the correct coloring for perception by the human eye requires precise control. Consequently, color printers are more expensive than grayscale printers and full-color printers are more expensive than duotone or highlight printers. Thus, one way in which printing operations may control costs is to purchase and use only grayscale or duotone printers. While duotone printers do not provide full-color capability, they do provide for the provision of some color in documents and at the same time support grayscale printing. Thus, only one type of printer is required to print both grayscale and limited color documents and some printing operations elect to forgo full color printers as a result.
For printing operations that need to print full color images, a full color printer is required. A full color printer may also be used to generate grayscale images since the black channel of a CMYK printer may be used alone to generate grayscale images. However, full color printers may not be used to generate duotone documents because rarely are the one or two colored inks used for duotone images one of the cyan, magenta, or yellow inks used in a typical four color printer. As duotone printing is adequate for many color applications, some printing operations relay on a duotone printer alone to support both grayscale and duotone printing.
To enhance the capability of duotone printers, numerous attempts have been made to map full color hues and shades to duotone printer color spaces. While a number of these schemes are somewhat successful, none can exactly match full color images with the duotone process because the gamut of colors possible with the CMYK process is larger than the gamut of possible colors with the duotone process. Consequently, some different hues and shades from a full color image are mapped to the same duotone hue and shade and color detail is lost. Consequently, many printing operations try to meet the need for grayscale, duotone, and full color documents with a duotone printer that is capable of converting full color images to duotone images, although full color images cannot be truly replicated on a duotone printer.
There is a need, therefore, for a system and method that prints grayscale, duotone, and true full color images with a single printer.